HOW LARGE ARE LEARNING EXTERNALITIES?*
通过校准增长模型，估计了学习外部性的大小，发现人力资本的社会回报率（9.0%）显著高于私人回报率（6.6%），表明学习外部性是经济增长的重要来源。
The quantitative features of human capital externalities are not fully understood. Although static externalities are estimated in some studies, learning externalities remain mostly unestimated. By calibrating a growth model, this article provides an estimate of learning externalities. The calibration uses an equilibrium condition that equates private returns on physical capital and human capital. The results suggest that sizable learning externalities exist, even in a conservative setup. The estimated social rate of return on human capital is 9.0%, compared to the private rate of return, 6.6%. Therefore, human capital externalities are an important source of economic growth.